190 LEWIS. GEOLOGY. 



matter consists of clay and of clay-marie, together 

 with a mixture of rolled stones of different kinds, but 

 always, I believe, of quartz, felspar, and the several 

 varieties of gneiss. Thus they seem at least to derive 

 their origin from the waste of mountains of gneiss. But 

 they do not lie in the vicinity of the mountainous district, 

 being, on the contrary, visible only towards the north 

 end of the island, where their broken and mouldering 

 edges may be traced and measured on the shores. At 

 Ness, Dale, and Leanol, they are from fifty to seventy 

 feet or upwards in thickness ; and repose, where their 

 contact can be observed, immediately on the gneiss which 

 forms the substratum of almost the whole country ; the 

 rock immediately subjacent being generally in a rotten 

 and mouldering state. 



With one or two exceptions, there is little to be re- 

 marked respecting the rocks that constitute this island, 

 which has not already come before the reader. Gneiss 

 is the predominant and fundamental rock ; and I shall 

 briefly notice such circumstances with regard to it as 

 have not occurred on former occasions, or have occurred 

 in a form less distinct. Every thing is worthy of attention 

 which conduces to the due knowledge of any one rock ; 

 since it is only by comparing the several forms, acci- 

 dents, and connexions under which it is displayed, that 

 a thorough knowledge of its natural history can be 

 obtained ; a knowledge which, extended to all the objects 

 in this tribe of substances, constitutes that science of 

 which we are in search. 



The cliffs in various parts of the coast, at the Gallan 

 Head, in the great Bernera, near Loch Carlowa, at the 

 Butt and from it to Tolsta Head, and again from 

 Stornoway to Loch Brolum, offer innumerable examples 

 of the passage of granite veins and of the contortions of 

 the gneiss. I have delineated a few, partly on account 

 of their singularity, partly because they serve to show 

 the changes which the rock must have undergone, and 



